INFRARED PHOTOEMISSION OF HOLES FROM ULTRATHIN (3-20 NM) PT/IR-COMPOUND SILICIDE FILMS INTO SILICON

The infrared responsivity is measured at low temperature on Schottky barrier detectors having ultrathin (3-20 nm) PtSi, IrSi, and compound silicide films as a metal electrode on p-type silicon. The total yield for internal hole photoemission is 1% per incident photon for PtSi and 0.1% for IrSi at a wavelength of lambda = 4-mu-m. The cut-of wavelengths are lambda = 5.4-mu-m and lambda = 8.2-mu-m for PtSi and IrSi, respectively. The compound silicides fabricated by sequential evaporation of Pt and Ir and subsequent annealing at T = 450-degrees-C show characteristics identical to that of PtSi. A Monte Carlo computer modelling is performed to simulate the scattering mechanisms in the thin silicide film leading to hole photoemission across the Schottky barrier into silicon. The optimum emission yield is observed for ultrathin films of the order of a few nanometers. The optimum film thickness is close to the escape depth d(esc) almost-equal-to 2-3 x L(el) almost-equal-to 5 nm which scales with the mean free path L(el) for quasi elastic scattering. The enhancement of the internal photoemission in ultrathin silicide films is predominantly due to the increase of the optical photoexcitation density rather than to an increase of the electrical emission yield in thin films.